Slight quivering of lips may be normal in babies. If her development is normal you need not worry. Bluish discoloration of lips is usually due to heart problem. But it is unlikely to affect only lower lip. Perhaps you are over anxious. If she is feeding well and gaining weight normally I do not think there is any problem. You can show her to your pediatrician
during next visit and tell him about these things. If he has any doubt he will take a cardiologist/s opinion.